For retracting gingiva from a prepared tooth a cord can be used. In this respect, a retraction cord is packed between gingival tissue and the margin of the prepared tooth (this region is also often called sulcus) using an appropriate dental instrument. To obtain sufficient vertical and horizontal retraction of gingival tissue, it is often necessary to pack several lengths of retraction cord into the sulcus in order to be able to make a detailed dental impression.
A description of the background in regard to retraction cords can be found e.g. in U.S. Pat. No. 4,522,593.
Generally, dental retraction cords are sometimes difficult to place into the gingival sulcus. The procedure can also be time consuming. It can also be cumbersome to remove the retraction cord prior to taking the impression. Coagulated blood may adhere to the cord and removing it may open the wound again which results in bleeding.
For a more convenient placement retraction pastes have been suggested.
A commercially available product to be used for retraction is sold under the name Expasyl™. However it is reviewed, that Expasyl™ is only effective under specific, limited conditions when the sulcus is flexible and of sufficient depth. The paste's thickness makes it difficult for some evaluators to express it into the sulcus. Moreover, according to the instruction of use, the viscosity of the composition might change when fluids like water, saliva or blood are absorbed.
Generally, removing non-hardening pastes completely out of the sulcus before taking the impression can be very time consuming and cumbersome. Usually, the paste is rinsed off using water-spray. However, sometimes paste residues are located deep in the sulcus and are thus difficult to remove. These residues might prevent the impression material from flowing into the sulcus area and may negatively influence the setting of the impression material which is subsequently applied. Moreover, after rinsing off the paste with water an additional drying step might be required before the impression can be taken. These removing and drying steps could cause bleeding of the tissue and might make an impression taking step more complicated.
Hardening materials are sometimes easier to remove. However, they are not very hydrophilic. This might cause problems with regard to flowability of the material into the gingival sulcus.
U.S. Pat. No. 5,362,495 refers to a method for widening the gingival sulcus without bleeding or oozing, comprising inserting within the gingival sulcus a material in the form of a biocompatible paste which is injectable for external use and having a plastic viscosity measured at 20° C. between about 13,000 and 30,000 Pa*s, wherein said material consisting of a material selected from the group of white clay, seaweed meal and mixtures thereof.
JP 2006056833 relates to a paste consisting of an astringent and filler containing clay mineral, torque, Mica, kaolin and/or montmorillonite.
US 2008/0220050 (Chen) relates to a composition for gingival retraction. The pasty composition contains water, clay, glass filler and astringent
WO 2006/057535 (Kim) describes a composition comprising a certain amounts of kaolin clay, water, aluminium chloride hexahydrate, starch powder, silicone oil and coloring agent.
US 2005/008583 (White) describes a gingival retraction material comprising a carrying medium, a retraction medium and an anti-evaporating component. As an example the following material formula is given: kaolin powder (80 wt.-%), aluminium chloride (15 wt.-%), water/glycerine sufficient to produce a heavy plastic consistency, flavorings/colour as desired.
US 2005/0287494 (Yang) describes a gingival retraction material prepared by using fibrillated fibers to improve viscosity and combining taste-modifying agent, color agent and kaolin filler to form a paste-like structure having the viscosity ranging from 31.0*106 cP to 71.0*106 cP.